# Queries to update a given index and find gcd in range in C++

In this tutorial, we will be discussing a program to find queries to update a given index and find gcd in range.

For this we will be provided with an array containing integers and Q queries. Our task is to find the result of given queries (updating a given value by X, finding the gcd between two given values).

## Example

Live Demo

#include <bits/stdc++.h>
using namespace std;
//getting middle index
int findMiddle(int s, int e) {
return (s + (e - s) / 2);
}
//updating values at given indices
void updateIndexValue(int* st, int ss, int se, int i, int diff, int si) {
if (i < ss || i > se)
return;
st[si] = st[si] + diff;
if (se != ss) {
int mid = findMiddle(ss, se);
updateIndexValue(st, ss, mid, i, diff, 2 * si + 1);
updateIndexValue(st, mid + 1, se, i, diff, 2 * si + 2);
}
}
//finding gcd values in the given range
int findGCDRange(int* st, int ss, int se, int qs, int qe, int si) {
if (qs <= ss && qe >= se)
return st[si];
if (se < qs || ss > qe)
return 0;
int mid = findMiddle(ss, se);
return __gcd(findGCDRange(st, ss, mid, qs, qe, 2 * si + 1),
findGCDRange(st, mid + 1, se, qs, qe, 2 * si + 2));
}
int findingGCD(int* st, int n, int qs, int qe) {
if (qs < 0 || qe > n - 1 || qs > qe) {
cout << "Not valid input";
return -1;
}
return findGCDRange(st, 0, n - 1, qs, qe, 0);
}
void updatingAllValues(int arr[], int* st, int n, int i, int new_val) {
if (i < 0 || i > n - 1) {
cout << "Not valid input";
return;
}
int diff = new_val - arr[i];
arr[i] = new_val;
updateIndexValue(st, 0, n - 1, i, diff, 0);
}
int calcGCDIndex(int arr[], int ss, int se, int* st, int si) {
if (ss == se) {
st[si] = arr[ss];
return arr[ss];
}
int mid = findMiddle(ss, se);
st[si] = __gcd(calcGCDIndex(arr, ss, mid, st, si * 2 +1),
calcGCDIndex(arr, mid + 1, se, st, si * 2 + 2));
return st[si];
}
int* calculatingGCD(int arr[], int n) {
int x = (int)(ceil(log2(n)));
int max_size = 2 * (int)pow(2, x) - 1;
int* st = new int[max_size];
calcGCDIndex(arr, 0, n - 1, st, 0);
return st;
}
int main() {
int arr[] = { 2, 5, 16, 7, 9, 23 };
int n = sizeof(arr) / sizeof(arr[0]);
int* st = calculatingGCD(arr, n);
cout << findingGCD(st, n, 2, 5) << endl;
return 0;
}

## Output

1

Updated on: 19-Aug-2020

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